I use vertical polarization for my client-accessed AP antennas. The bridge polarization depends on the height and terrain. Usually I use VP over land, and HP over water. I live and work on the beach. Lucky me!
Use sector antennas if you can. I use omnis only in areas where the homeowner’s association prohibits multiple sector-type antennas.
I buy my antennas from HyperLink (sectors) and Pacific Wireless (omnis). I noticed there are a few suppliers in the US that will ship worldwide, with a few countries on the exception list.